During the coming year we will continue to focus our major efforts on the analysis of sex determination in Drosophila. Our work on sex determination is divided between the molecular genetic of new functions involved in the control of sex. Our work on the first of these genes that we cloned (doublesex, dsx) will, in the immediate future, be focused on understanding the complex pattern of transcripts that are produced by this gene. We will sequence appropriate portions of cDNAs and the genome in order to define the exact differences between the different transcripts. To date we have identified several different internal splice options that are used as well as two different 3' ends. It seems likely that at least one transcript has a 5' end different from that of the other transcripts. When portions of the genome that are unique to each transcript are identified we will make probes (both labeled nucleic acid and antibodies) to examine the pattern of usages of the different gene products temporally and spatially. We have sequenced one cDNA that appears to have a complete open reading frame and are in the process of expressing it in E. coli in order to begin a set of experiments aimed at inquiring whether it is a DNA binding protein and whether in interacts with sequences in or near sex specific differentiation functions known to be under dsx control. The tra-2 gene has also been recently cloned in our laboratory and substantial efforts during the coming year will be directed at it basic characterization. Our initial analyses of mutants in and around tra-2 and its transcription pattern suggest that it is at least 10 kb in size and transcriptionally complex. We will also be undertaking molecular screens aimed at isolating both new sex determination regulatory genes and new sexual differentiation functions in the next couple of months. Genetic analyses are being carried out on new female lethal locus on the X chromosome and on the intersex gene. In addition several potential new sex determination regulatory genes have been cloned based on their extensive homology with dsx sequences (referred to as dsx cognates, dsc s). Mutants in the gene that we believe corresponds to one dsc have been isolated and shown to interact with mutants at other genes known to be in sex determination.